Techniques for integrating a metal and a resin with each other are demanded in a wide variety of fields such as those of manufacturing parts of automobiles, domestic electrification products, industrial equipment, etc. For this purpose, many adhesives have been developed. Among them are very excellent adhesives. Adhesives that exhibit their function at ordinary temperature or upon heating are used for bonding to integrate a metal and a synthetic resin with each other. The bonding method using such an adhesive is now a common technique.
Meanwhile, researches have heretofore been made to find an even more rational bonding method that does not use an adhesive. However, a method of integrating a high-strength engineering resin with light metals such as magnesium, aluminum and alloys thereof or iron alloys such as stainless steel without using an adhesive has not yet been put to practical use. Examples of such a method include a method wherein a resin component is bonded (fixed) to a metal by injection molding or other similar process. This method is defined and named by the present inventors as “injection bonding method” (it should be noted, however, that the term does not mean only a forming method effected by injection molding).
The present inventors conducted exhaustive studies and development and found that bond strength increases uniquely (in the present invention, the term “bond strength” is used as a synonym of “adhesive force”) if a shaped aluminum alloy material is dipped in an aqueous solution of a water-soluble reducing agent and thereafter brought into contact with a thermoplastic resin composition consisting essentially of an alkylene terephthalate resin under high-temperature and high-pressure conditions. The present inventors proposed this finding as Japanese Patent Application Laid-open No. 2003-103563.
The present inventors noted aluminum alloy, in particular, among metal alloys for the reasons stated below. Aluminum is light in weight and abundant as a resource. Alloying or surface treatment allows aluminum to exhibit high strength, high corrosion resistance, free-cutting properties, high extensibility, etc. in addition to its inherent physical properties, i.e. excellent extensibility, electrical conductivity and thermal conductivity. Therefore, aluminum alloys are now used in a wide variety of fields. Particularly, it is expected that personal computerization will further progress and, consequently, mobile electronic devices will be used for general purposes in the future. Accordingly, it is expected that there will be an even stronger demand that these devices should be reduced in weight. In this regard, the utilization of aluminum alloys is expected to further increase.
The present inventors focused on aluminum alloy and a thermoplastic resin composition mainly containing polybutylene terephthalate (hereinafter referred to as “PBT”), among the above-described inventions made by the present inventors, and repeated experiments regarding the horizontal development relating to the above-described invention. The feature of the above-described invention resides in that an aluminum alloy is treated with an aqueous solution of a water-soluble reducing agent. It was, however, observed by surface analysis and so forth using X-ray photoelectron spectroscopy (XPS) that even if a reducing agent was used, when the aluminum alloy was taken out of the treating aqueous solution, the surface thereof was instantaneously oxidized by oxygen in the air and not in a zero-valence aluminum metal state in terms of the final surface condition.
Meanwhile, hydrazine used mainly in the above-described invention is not particularly dangerous. However, we also considered it to be important to find other effective chemicals for surface treatment. With these matters taken into consideration, we hypothesized about the injection bonding principle and performed demonstrative experiments. This was done because we considered it to be useful for developing a reliable injection bonding method.
The present inventors made efforts to expand the above-described invention achieved by us to develop a method capable of attaining the same purpose by treating the surface of an aluminum alloy without using a reducing agent such as hydrazine, sodium borohydride (NaBH4), which is costly, or lithium aluminum hydride (LiAlH4), which is difficult to handle.
There are various kinds of aluminum alloy improved in strength or other properties. There has also been a need of a pretreatment method capable of bonding a resin to an aluminum alloy containing magnesium, silicon, copper or other metal with satisfactory injection bond strength.
An object of the present invention is to obtain an aluminum alloy-and-resin composite wherein a thermoplastic resin composition and a shaped aluminum alloy material are made to adhere so strongly that they will not readily separate from each other by treating the aluminum alloy surface, and also obtain a production method therefor.
Another object of the present invention is to obtain an aluminum alloy-and-resin composite capable of making housings and parts of various devices, structures, etc. free from problems in terms of configuration, structure and mechanical strength, and also obtain a production method therefor.
Still another object of the present invention is to obtain an aluminum alloy-and-resin composite useful for reducing the weight of housings and parts of electronic devices, structures, etc. and for simplifying device manufacturing processes, and also obtain a production method therefor.